Method of producing lactic acid esters



Patented Mar. 30, 1943 N'l' OFFICE METHOD OF PRODUCING LACTIO ACID ESTERS George Gordon Urquhart, Cynwyd, Pa.

No Drawing. Application December 13,1940, Serial No. 369,955

4 Claims.

My invention relates to a new process for the production of lactic acid esters. More particularly, my invention relates to an improved process for making glycerol lactates and lactic acid esters of dihydric and polyhydrie alcohols. It has been shown in United States Patent No. 2,181,231 that glycerol esters of lactic acid can be made by esterifying glycerol with various proportions of lactic acid. The products thus obtained are glycerol monolactate, glycerol dilactate, glyceryl lactate and glycerol lactyllactates. These esters can be employed in the manufacture of alkyd resins and confer valuable properties to the coating compounds made therefrom. The aforementioned process has certain inherent disadvantages with respect to cost and purity of product. Lactic acid of sufficient purity costs more than When the alkali metal or alkali earth lactates are employed for the preparation of glycerol-lactic acid esters, in accordance with my invention, it is not essential to resort to expensive purification processes because unreactive impurities can be separated by filtration along with halide salt which is formed during the reaction. Such a purification step is not feasible when lactic acid is esterified directly. Lactic acid cannot be purified by distillation and in order to elfect its purification it must be either converted to an ester e. g. methyllactate, or it must be converted to a lactide. Both of these processes are costly and time consuming.

The chemical reactions involved in the preparation of glycerol dilactate, in accordance With my invention, may be set forth as follows:

GHiOl CH2OOC.CHOH.CH3

NaOOQCHOlELOHa I CHOH 0H0 +(2NaCl) I NaOOC.CHOH.CH3 I CHiCl CH2OOC.CHOH.CHa (1,3 dichloro- (sodium lactate) (glycerol dilactatc) (sodium chloride) propanol-2) either glycerol or phthalic anhydride and consequently lactic acid would not be used extensively;

or at all in producing 3-component alkyds be cause of this fact. Furthermore, technical grades of lactic acid contain protein and metallic impurities which tend to discolor the glycerol-lactic acid esters.

In my newprocess, I use neither lactic acid nor glycerol for the preparation of glycerol lactic acid esters. Instead, I prefer to use the intermediate chemicals leading to these two prodpotassium,

. Instead of the sodium salt it is possible to use other alkali metal or alkali earth salts, such as calcium and barium lactates. Of these salts, I prefer to employ the sodium and calcium lactates, the calcium salt having the advantage of being bivalent and inexpensive, while the sodium salt react more readily than the calcium salt and involves no difficulty in removing the sodium chloride and other impurities from the reaction mass.

Glycerol lactate monochlorohydrin can be ucts. Thus, great economies in the cost of manmade in a similar fashion by condensing only one ufacture of alkyd resins can be effected. At the mole of sodium lactate with one mole of 1,3 disame time, my process leads to the production of chloropropanol-Z to give substantial yields. It lighter colored glycerol lactates. is then feasible to react the second halogen atom In accordance with my invention, I condense with alkali metal or alkali earth salts of other 1,3 dichloropropanol-2 with an alkali metal or acids, such as adipic,-ricinoleic and tartaric.

CHzCl ment with sodium carbonate or lime respectively. Solutions of these salts of lactic acid can be obtained in any desired purity in accordance with well established procedures.

I have found that it is also practical to make glycerol lactates by condensing one mole of 1,3 dichloropropanol-2 with either one mole of calcium lactate or two moles of sodium lactate, plus one mole of lactic acid. This may be exemplified as follows:

NaOOC.CHOH.CHa

(311201 NaOOC.CHOH.CHa CH2OOC.CHOH.CH3 (CHOH +(HOOC.OHOH.CHa (BHOOCCHOILOHs +(2NaCl) propanol-2 with three moles of sodium lactate for the manufacture of plastics, can be prepared in accordance with the following reaction:

( am 3111 j on +(NaOOC.CHOH.GHi)= .CHfji GHzCl (Allyl chloride) I have also found that chloro alkanes may be used to advantageinthe preparation of lactic acid esters. Thus dichlor-oethane may be condensed-with two moles of sodium lactate to prosodium lactate) (aliyl lactate) duce 'a valuable plasticizer, glycol dilactate, as

shown'belowrsop acetate) (oniooojonoircm 011201 moooono'rtom om ooccnoucm (Dichldrothzne) (sodiunilactate) (glyco1'dilactate) I The following examples are used to illustrate the pri nciples of invention and it is to be clearly understood that thefproportions of materials, temperatures .ot reaction, and the method .of isolating the productslmay be varied Wid y without departing from thespiritjand scope of my invention.

Example 1 1h" a one litrthie-necked round bottom flask fitted with a liquidesealed stirrer and reflux condensemareplacd ize'grains u" mole) of 1,3 diohloropfopanol zzand 373 (2 moles) of a 60% aqueous solution of sodium lactate. The. mixtureis heated by means of an oil ating column is placed 129 grams (1 mole) of 1,3

dichloropropanol 2. The flask is heated by means of an oil bath while 3'73 grams (2 moles) of a 60% aqueous solution of sodium lactate is added 7 )+NaCi 01110000110121.0113

(NaCl) by means of a dropping funnel with a large bore delivery tube. The rate at which the solution of sodium lactate is added is such that the water is distilledfrom the reaction mass at about .the same rate at which it is added. When all the sodium lactate solution has been added, the heatof Examples 1 and 2-,an excess of 1,3 dichloropropanol:2 is used. The reaction is continued for 'three hours and the excess 1,3 dichloropropanol 2 bathjmaintained at a temperature. of approxi i mately160. degrees C and stirred while refluxing for a period. of threehours. By thattime a considerable-amount of sodium chloride v.willhave separated. a

The water istheri adjusted in the reflux condensertoallow water vapor to be expelled. The temperature of the oil; bath maybe raised to increase the rate of the removal of water by distillation. When no more sodium chloride separates, the reaction Jmass is .filtered while still warm by means 0f,.the,s,u ction filteix The product, which in this example would, be glycerol dilactate, .is a clear viscous liquidwith' a slight'ambe'r tinge and is suitable for use in-the formation of alkyd resins 7 As illustrating amethod'of employingthe glycerol, dilactate produced in accordance with the foregoing Example 1, in the production of an alk iIthe following procedure may be carried out; The esterification of the glycerol dilactate as prepared in the preceding example is accomplished by mixing two equivalents of the glycerol dilactate and three-equivalen'ts of a dicar boxylic acid,. such .as' sebacic acid, in a, threenecked fiask-fittedwith a carbon dioxide inlet capillary and thermometer, which dips into the reaction mixture; anda short necked distilling head which in turn is connected to' the condenser and -rem-giver. The flask is heated'with an oil bath to maintain a temperature in the flask of with any water which may be present is distilled under-vacuum to leave glycerol dilactate and sodium chloride which is then filtered and the glycerol dilactate recoveredas given in the preceding examplesr n I v Example 4;'In-' the apparatus" described in previous'example's' is placed- 1 mole of 1,3 dichloropropanol 2"and a' molal-quantity of dehydrated, powdered calciumlactate is slowly added. The reaction requires more time than with sodium lactate and in order to facilitate theseparation of the calcium chloride, sodium carbonate may be added to the product, after which 1tshe glycerol dilactate may be obtained by filtraion. 7 1

In the Example 3, involving the use of an excess of a halogeno compound and thendistilling such excess from the vessel, I have found that the reaction time may be reduced considerably. The halogeno compound is recovered and added to the next batch with the addition of an amount of fresh halogeno compound as may be required to give the requisite quantity. By shortening the reaction time, I have found that the resultant esters are lighter in colon, Furthermore, I pointout that this procedure is unlike the esterification of lactic acid with polyhydric alcohols, since it is here possible to remove easily the excess of V which may have been rendered insoluble by this approximately 180 degrees C. During the course electrolyte. V A

What is claimed as newand useful is: 1 1. A process for the production of laotic'acid 4. A process for the production of glycerol dilactate which comprises condensing 1 mole of 1,3-dichloropropanol-2 with 2 moles of an alkali salt of lactic acid containing about 40% by weight of water, refluxing the ingredients until the reaction is complete, and then distilling ofi the water and filtering off the precipitated alkali chloride along with any other insoluble impurities.

GEORGE GORDON URQUHART. 

